Hello Panka,
I have been using Cognos products for quite some time now. Upfront it a
great tool for more Management Reporting - give the ability to take a TON
of data, build a muti dimensional cube and serve it up to end user at a
high level view in which they can the drill into the detail if need be,
twist and turn the data and nest dimensions within dimensions.

Reportnet is more of a real report writing tool - give the ability to have
very detailed report (Upfront hates detail performance wise). as well as
give you multiple ways of distribution (pdf, email, bursting to email,
excel etc). ReportNet also is great if you need to report from databases
on different platforms. ReportNet comes in many different levels of the
tool for the basic end user who doesn't know much about reporting tools to
the developer who can write and distribute very complex reports.

First of all, I should clarify that ReportNet is a suite of products in a particular architecture, primarily server-side web applications. At present, the set contains Cognos Connection, a web portal; Framework Manager, metadata modelling (and the only client-side application in the suite); Query Studio for simple ad hoc querying; and Report Studio for more complex reports. You should note that Report Studio is the ReportNet equivalent of Impromptu and is meant for reporting down to transaction level. It is NOT an OLAP tool.

PowerPlay is a different product again. At present, it is part of the Series 7 suite though I have heard rumours that there will be a ReportNet equivalent some time next year. PowerPlay is an OLAP tool and is not meant for transaction level reporting, although it can be used for that (but you start to get build time and performance issues the larger your cubes become).

Which tool you choose depends on what you're trying to do. If you want to do multi-dimensional analysis, go for PowerPlay. If you want reporting at transaction level with sophisticated layout features, go for ReportNet. You should also know that ReportNet requires some hefty infrastructure for the server components, while PowerPlay can be used as a client application. Also, as PowerPlay involves data organised into multi-dimensional cubes for analysis, it can never give you real-time data. The ReportNet tools can be used on an ERP database as well as a data mart or data warehouse, so can give real-time reporting capability. Both can access separate data sources, though they handle the issues differently.

I should also clarify that Upfront is the web portal for the Series 7 suite (and earlier) - it is NOT a reporting tool at all. PowerPlay cubes can be published to either Upfront or Cognos Connection, although you will need PowerPlay web to use them on a web portal. PowerPlay cubes can "drill through" to either Impromptu or Report Studio reports for transaction level detail should you wish.

In answer to your questions below, the "number of dimensions and measures" is not really an issue at all. For multi-dimensional analysis in general you will need to have hierarchical dimensions, otherwise you may as well just have a report listing. It is true that the more dimensions and measures you have in a cube the bigger and more complex the cube will be, which will be an issue both in terms of build time, performance for the end user, and the difficulty for the user to comprehend. It's not an issue of capability for the products but of usability.

If you want to find out more, there are a lot of production information sheets and white papers on the Cognos website.

Now keeping in mind the design of reports we have to do I have one more
question:

Is it possible to perform dimensional analysis (higher level) in a cube
and then to "drill through" to a ReportNet report to find transaction
level data. i.e. can we combine the functionality of PowerPlay and
ReportNet.

To make it more clear:
Can we perform an analysis so that, say, country level details (higher
levels) are available in PowerPlay and ZIP wise details (lowest level)
are in ReportNet.